A 340 GHz 4 × 4 detector array based on 0.18 µm gallium arsenide technology is presented. Each pixel is composed of a planar log-periodic antenna, a Schottky barrier diode, and a pair of bonding pads. The detector array is mounted on a silicon lens and assembled onto a PCB using the authors’ novel flip-chip structure. Off-axis performances of the lens-coupled detector array are demonstrated experimentally, which agree well with the simulated ones. The detector array shows a peak voltage responsivity of 1347 V/W and a noise equivalent power of 2.1 pW/Hz1/2 at 340 GHz, exhibiting much better performance than the CMOS counterpart.