A compound semiconductor device includes: a carrier transit layer; a carrier supply layer over the carrier transit layer; a source electrode and a drain electrode above the carrier supply layer; a gate electrode above the carrier supply layer between the source electrode and the drain electrode; and a first insulating film and a second insulating film above the carrier supply layer between the gate electrode and the drain electrode. The gate electrode includes a portion above the second insulating film, the second insulating film covers a side surface of the first insulating film from the drain electrode side, and a second concentration of electron traps in the second insulating film is higher than a first concentration of electron traps in the first insulating film.