To provide a semiconductor device for spectral diffusion type radar systems in which any virtual image signal due to a nonlinear component of an active device is inhibited.

In this semiconductor device for spectral diffusion type radar systems (back diffusions modulator 133), (a) unbalance/balance converting circuit 162 which consists of joint line (lines 162a and 162b) and joint line (lines 162c and 162d) to convert receive signal input as unbalance signal into a pair of balance signals and (b) balanced type back diffusion circuit 161 provided with a switching circuit consisting of one or more transistors (transistors Q1, Q2, Q3 and Q4) which diffuses the pair of balance signals backward through the switching circuit by using pseudo noise codes input as a differential signal by the same code series of pseudo noise code, input by the pair of balance signals output from the unbalance/balance converting circuit 162 as a differential signal, are formed on the same semiconductor substrate.