In this paper, a novel design of a high-gain and wideband slot antenna operating at V-band is presented. The gain and bandwidth enhancements are achieved by feeding a simple radiating slot with a ridge-gap waveguide and placing a single layer superstrate above the antenna. The superstrate acting as a partially reflective surface is based on complementary frequency selective surface which provides positive phase gradient over the frequency range 47 to 65 GHz. Numerical simulations of the proposed design demonstrate a gain enhancement of 8.3 dB at 63 GHz when compared with the antenna without the superstrate, and 3-dB gain bandwidth of about 5 GHz. Moreover, the antenna is matched to the feeding ridge-gap waveguide over the frequency range of 56.0 to 66.7 GHz.