A low profile CPW fed millimeter wave rectangular slot antenna operating with a wideband; centered at 94 GHz has been designed, fabricated and tested on a 10 μm silicon diaphragm. To improve the bandwidth of the conventional slot antenna a C-shaped tuning stub has been incorporated. Measurement results show that the antenna operates from 75 to 105 GHz with a reflection coefficient better than -10 dB. At its resonant frequency the fabricated slot antennas have a reflection co-efficient ranging from -25 dB to -35 dB. The bandwidth of the antenna with a tuning stub was found to be over 30% at -10 dB. By using the slot antenna with a C-shaped tuning stub the bandwidth has been shown to improve, which could be used for several Millimeter wave applications.