PURPOSE: To prevent positional deviations of a gate electrode and an interelement isolation layer to an ohmic electrode due to positional deviation, etc., of a mask alignment by forming the layer and the gate electrode in a self-alignment manner.

CONSTITUTION: A structure 66 on the way of forming an ohmic electrode provided on a base 48 having an active layer on a surface is used as a mask, the base 48 is ion implanted to form an interelement isolation layer 68. Two ohmic electrodes 70 having a shape of a section perpendicular to a surface of the base 48 has an inverted tapered shape are formed from the structure 66 on the way of forming the ohmic electrodes along a gate length direction through a gate electrode forming region. Then, with the electrodes 70 as masks a gate electrode having a gate length of an interval between the electrodes 70 is formed on the base 48 of a region interposed to be held between the electrodes 70.