The semiconductor device

A semiconductor device having a through-hole structure and constituting a III-V nitride semiconductor, comprising: forming on a conductive substrate (11) high impedance Al x Ga 1- x N constituting the buffer layer (12); having a channel layer formed on the buffer layer (12) and the N-type GaN undoped Al y Ga 1-y N constituting element forming layer (14); selectively formed on the forming (14) a source electrode (16) in the element, the drain electrode (17) and the gate electrode (15). And (11) is electrically connected to the source electrode and the conductive substrate (16) forming a layer (14) through holes (12a) provided on (12) and the element is filled by the buffer layer. Thus, by simultaneously preventing the leakage current is generated in the substrate and the semiconductor layer is formed between the through hole becomes easier to obtain a high-frequency characteristics, high output characteristics and power characteristics.