To provide a semiconductor device manufacturing method by which the high-frequency characteristic of a field effect semiconductor device can be improved by shortening the length of a gate and, at the same time, reducing the capacitances of the gate and a drain, without increasing the resistance of the gate.

After an SiO2 film 3 is formed on a GaAs substrate 1, a photoresist film 4 having an opening at the forming position of a gate electrode is formed. Then, the SiO2 film 3 is etched until the substrate 1 is reached while the substrate 1 is set in a way such that the normal line to the substrate 1 is inclined by about 20° from the direction in which the etching rate becomes faster by using an etching system having high anisotropy to the SiO2 film 3 and a gate-forming metal is vapor-deposited on a photoresist 4 formed on the film 3 from the direction perpendicular to the substrate 1. Then, a gate electrode 7 is formed by removing the metallic film 6 and the SiO2 film 3 by the lift-off method.