Electrode pad on conductive semiconductor substrate

An electrode pad on a semiconductor substrate is provided. The pad has a small capacitance on an electrode pad part, and permits characteristic impedance of the electrode pad having a practical size to be controlled. On an n-InP substrate (1), a mesa stripe type optical waveguide is formed by stacking a clad layer (2), an i layer (3), a p-InP clad layer and a p-type contact layer (4), and in the vicinity of the optical waveguide, an insulating material film (8) having a mesa-shaped deposited part (8c) is formed on the n-InP substrate (1). An electrode metal (11a) and wiring metals (11b, 11c) for supplying the optical waveguide with an electric signal are arranged on the optical waveguide and the insulating material film (8), respectively, and an electrode pad (10) is arranged on an upper plane of the mesa-shaped deposited part (8c) to have a prescribed interval (t1) (approximately 17-29mum) between the n-InP board (1) and the electrode pad (10).