A semiconductor device includes a semiconductor layer (1) containing GaN and an electrode. The electrode includes an electrode main body (6), a connection-use electrode (8) containing Al and formed at a position farther from the semiconductor layer (1) than the electrode main body (6), and a barrier layer (7) formed between the electrode main body (6) and the connection-use electrode (8), the barrier layer (7) containing at least one selected from the group consisting of W, TiW, WN, TiN, Ta, and TaN. A surface roughness RMS of the barrier layer (7) is 3.0 nm or less.