diff --git a/script/sync_components.py b/script/sync_components.py
index 3800d0f8..e0a07f76 100644
--- a/script/sync_components.py
+++ b/script/sync_components.py
@@ -1821,13 +1821,14 @@ def _convert_field(key: str, raw: dict, schema_dir: Path) -> dict | None:  # noq
     is_structural = entry_type == "pin" or bool(references)
     advanced = _classify_advanced(key, required=required, is_structural=is_structural)
 
+    default_value, gated_component = _extract_default(raw, key=key)
     entry: dict[str, Any] = {
         "key": key,
         "type": entry_type,
         "label": _key_to_label(key),
         "description": docs.text or None,
         "required": required,
-        "default_value": _coerce_default(raw.get("default")),
+        "default_value": default_value,
         "options": _build_options(raw),
         "allow_custom_value": False,
         "range": list(_DATA_TYPE_RANGE[data_type]) if data_type in _DATA_TYPE_RANGE else None,
@@ -1836,7 +1837,7 @@ def _convert_field(key: str, raw: dict, schema_dir: Path) -> dict | None:  # noq
         "depends_on": None,
         "depends_on_value": None,
         "depends_on_value_not": None,
-        "depends_on_component": None,
+        "depends_on_component": gated_component,
         "references_component": references,
         "pin_features": _resolve_pin_features(raw) if entry_type == "pin" else [],
         "pin_mode": None,
@@ -1969,6 +1970,31 @@ def _coerce_default(value: Any) -> Any:
     return value
 
 
+def _extract_default(raw: dict, key: str = "") -> tuple[Any, str | None]:
+    """Resolve ``(default_value, depends_on_component)`` for a field.
+
+    Reads ``default_with`` (``cv.OnlyWith``, esphome/esphome#16276)
+    in preference to plain ``default``. ``default_without``
+    (``cv.OnlyWithout``) has inverse-gate semantics that
+    ``depends_on_component`` can't model — no default surfaces for
+    those fields. Multi-component ``default_with`` picks the first
+    component and logs a warning (no upstream call site uses a
+    list today). *key* is the field name for the log context.
+    """
+    if (gated := raw.get("default_with")) is not None:
+        components = gated.get("components") or []
+        if len(components) > 1:
+            _LOGGER.warning(
+                "%s: default_with with multiple components %s; only "
+                "the first (%s) will be used as depends_on_component.",
+                key or "<unknown>",
+                components,
+                components[0],
+            )
+        return _coerce_default(gated.get("value")), components[0] if components else None
+    return _coerce_default(raw.get("default")), None
+
+
 def _resolve_use_id_reference(raw: dict) -> str | None:
     """Map ``use_id_type: 'ns::Class'`` to a component domain.
 
diff --git a/tests/test_sync_components_default_extraction.py b/tests/test_sync_components_default_extraction.py
new file mode 100644
index 00000000..a7bac124
--- /dev/null
+++ b/tests/test_sync_components_default_extraction.py
@@ -0,0 +1,191 @@
+"""Tests for ``_extract_default`` and the ``_convert_field`` end-to-end.
+
+Covers both the resolver and the full conversion pipeline against
+real raw-schema fixtures captured from
+``script/build_language_schema.py`` post esphome/esphome#16276.
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+import pytest
+
+from script.sync_components import (  # type: ignore[import-not-found]
+    _convert_field,
+    _extract_default,
+)
+
+
+def test_unconditional_default_returns_value_and_no_gate() -> None:
+    """Plain ``default: "..."`` flows through unchanged."""
+    assert _extract_default({"default": "true"}) == (True, None)
+    assert _extract_default({"default": "False"}) == (False, None)
+    assert _extract_default({"default": "5"}) == ("5", None)
+
+
+def test_no_default_returns_pair_of_nones() -> None:
+    """No ``default`` and no ``default_with`` → ``(None, None)``."""
+    assert _extract_default({"key": "Optional"}) == (None, None)
+
+
+def test_default_with_single_component_returns_value_and_gate() -> None:
+    """``default_with`` with one component → gated default."""
+    raw = {"default_with": {"value": "True", "components": ["wifi"]}}
+    assert _extract_default(raw) == (True, "wifi")
+
+
+def test_default_with_multi_component_picks_first_with_warning(
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Multi-component ``default_with`` → first component + log.warning.
+
+    No upstream call site uses a list today; pick the first and
+    log so the field still gets a default.
+    """
+    raw = {
+        "default_with": {
+            "value": "DC_SOURCE",
+            "components": ["zigbee", "nrf52"],
+        },
+    }
+    with caplog.at_level(logging.WARNING, logger="sync_components"):
+        value, gate = _extract_default(raw, key="power_source")
+    assert value == "DC_SOURCE"
+    assert gate == "zigbee"
+    assert len(caplog.records) == 1
+    msg = caplog.records[0].getMessage()
+    assert "power_source" in msg
+    assert "zigbee" in msg
+    assert "nrf52" in msg
+
+
+def test_default_with_empty_components_returns_no_gate() -> None:
+    """Empty ``components`` → value flows, gate stays None."""
+    raw = {"default_with": {"value": "True", "components": []}}
+    assert _extract_default(raw) == (True, None)
+
+
+def test_default_with_takes_precedence_over_default() -> None:
+    """``default_with`` wins when both are present."""
+    raw = {
+        "default": "False",
+        "default_with": {"value": "True", "components": ["wifi"]},
+    }
+    assert _extract_default(raw) == (True, "wifi")
+
+
+# Real raw entries captured from the patched build_language_schema.py
+# against ESPHome's tree. Pasted verbatim so the device-builder side
+# has a concrete contract to test against without needing the
+# upstream PR merged. The fixtures are the canary if the upstream
+# field name changes.
+
+_FIXTURE_SOFTWARE_COEXISTENCE: dict = {
+    "default_with": {"value": "True", "components": ["wifi"]},
+    "key": "Optional",
+    "type": "boolean",
+}
+
+_FIXTURE_POWER_SOURCE: dict = {
+    "default_with": {"value": "DC_SOURCE", "components": ["nrf52"]},
+    "key": "Optional",
+    "type": "enum",
+    "values": {
+        "BATTERY": None,
+        "DC_SOURCE": None,
+        "EMERGENCY_MAINS_CONST": None,
+        "EMERGENCY_MAINS_TRANSF": None,
+        "MAINS_SINGLE_PHASE": None,
+        "MAINS_THREE_PHASE": None,
+        "UNKNOWN": None,
+    },
+}
+
+_FIXTURE_TX_POWER: dict = {
+    "default_without": {"value": "3dBm", "components": ["esp32_hosted"]},
+    "key": "Optional",
+    "type": "enum",
+    "values": {
+        "-12": None,
+        "-3": None,
+        "-6": None,
+        "-9": None,
+        "0": None,
+        "3": None,
+        "6": None,
+        "9": None,
+    },
+}
+
+
+def test_extract_default_software_coexistence_fixture() -> None:
+    """Real ``software_coexistence`` raw entry."""
+    assert _extract_default(_FIXTURE_SOFTWARE_COEXISTENCE) == (True, "wifi")
+
+
+def test_extract_default_power_source_fixture() -> None:
+    """Real ``power_source`` raw entry — string default."""
+    assert _extract_default(_FIXTURE_POWER_SOURCE) == ("DC_SOURCE", "nrf52")
+
+
+def test_extract_default_tx_power_fixture_skipped_for_now() -> None:
+    """``default_without`` returns ``(None, None)`` — inverse-gate follow-up."""
+    assert _extract_default(_FIXTURE_TX_POWER) == (None, None)
+
+
+@pytest.fixture
+def schema_dir(tmp_path: Path) -> Path:
+    """Empty dir for ``_convert_field`` (only used for ``extends`` lookups)."""
+    return tmp_path
+
+
+def test_convert_field_software_coexistence_carries_gate_and_default(
+    schema_dir: Path,
+) -> None:
+    """``cv.OnlyWith(K, "wifi", default=True)`` → boolean entry, gated."""
+    entry = _convert_field("software_coexistence", _FIXTURE_SOFTWARE_COEXISTENCE, schema_dir)
+    assert entry is not None
+    assert entry["type"] == "boolean"
+    assert entry["default_value"] is True
+    assert entry["depends_on_component"] == "wifi"
+    assert entry["required"] is False
+
+
+def test_convert_field_power_source_carries_gate_and_string_default(
+    schema_dir: Path,
+) -> None:
+    """OnlyWith enum field with a string default — verifies no bool coercion."""
+    entry = _convert_field("power_source", _FIXTURE_POWER_SOURCE, schema_dir)
+    assert entry is not None
+    assert entry["default_value"] == "DC_SOURCE"
+    assert entry["depends_on_component"] == "nrf52"
+    option_values = {opt["value"] for opt in entry["options"] or []}
+    assert "DC_SOURCE" in option_values
+    assert "BATTERY" in option_values
+
+
+def test_convert_field_tx_power_default_without_no_gate(
+    schema_dir: Path,
+) -> None:
+    """``cv.OnlyWithout`` field → no default, no gate (follow-up)."""
+    entry = _convert_field("tx_power", _FIXTURE_TX_POWER, schema_dir)
+    assert entry is not None
+    assert entry["default_value"] is None
+    assert entry["depends_on_component"] is None
+    option_values = {opt["value"] for opt in entry["options"] or []}
+    assert "3" in option_values
+
+
+def test_convert_field_unconditional_default_unchanged(schema_dir: Path) -> None:
+    """Plain ``cv.Optional(K, default=True)`` flows through with no gate.
+
+    ``retain``'s ``_COMPONENT_GATED_KEYS`` membership applies in
+    ``_convert_config_vars``, not ``_convert_field``.
+    """
+    raw = {"default": "true", "key": "Optional", "type": "boolean"}
+    entry = _convert_field("retain", raw, schema_dir)
+    assert entry is not None
+    assert entry["default_value"] is True
+    assert entry["depends_on_component"] is None