Compound semiconductor device and method of manufacturing the same

A method of manufacturing a compound semiconductor device comprising:

• forming a compound semiconductor layer;
• forming a silicon nitride film on the compound semiconductor layer;
• forming a source electrode on the compound semiconductor layer adjacent the silicon nitride film;
• and
• forming a high-resistance layer comprising Al, Si, and N, the high-resistance layer being between the source electrode and the silicon nitride film and having a higher electric resistance value than the source electrode.

A power supply circuit comprising:

• a transformer;
• and
• a high-voltage circuit and a low-voltage circuit sandwiching the transformer, the high-voltage circuit comprising a transistor, the transistor comprising:
• a compound semiconductor layer;
• a first electrode and a second electrode formed on an upper side of the compound semiconductor layer;
• and
• a high-resistance layer disposed in a lower portion of the first electrode and higher in an electric resistance value than the other portions of the first electrode;
• wherein
• in the high-resistance layer, an Al content ratio gradually decreases from a value equal to or higher than 80% from an electrode end distant from the second electrode toward an electrode end close to the second electrode.