A W-band monolithic direct conversion receiver for passive millimeter wave imaging system using commercial 0.15 m GaAs pHEMT technology has been realized. The receiver module consists of a two-stage preamplifier, a zero bias detector and an low pass filter. The input return loss S11 over W-band was measured, and the estimated noise equivalent power (NEP) of the detector showed the value of 7.8 pW/√Hz. The measured responsivities of the proposed receiver showed the peak value of 1.31 kV/W and average value of 1.16 kV/W respectively. A low pass filter with preselected bandwidth of 2 GHz is integrated into the proposed chip to stable the output, and the receiver chip occupies the area of 2.26 × 0.68 mm 2 excluding test pads.