An insulating layer, an undoped first GaN layer and an AlGaN layer are laminated in this order on a surface of a semiconductor substrate. A surface barrier layer formed by a two-dimensional electron gas is provided in an interface between the first GaN layer and the AlGaN layer. A recess (first recess) which reaches the first GaN layer but does not pierce the first GaN layer is formed in a surface layer of the AlGaN layer. A first high withstand voltage transistor and a control circuit are formed integrally on the aforementioned semiconductor substrate. The first high withstand voltage transistor is formed in the first recess and on a surface of the AlGaN layer. The control circuit includes an n-channel MOSFET formed in part of the first recess, and a depression type n-channel MOSFET formed on a surface of the AlGaN layer. In this manner, there are provided a gallium nitride semiconductor device which can be used under a high temperature environment while reduction in total circuit size can be attained, and a method for producing the gallium nitride semiconductor device.