The tungsten-p type silicon point contact diode was investigated as a video detector from 90 GHz to 474 THz. The diode responsivity was examined with respect to the applied pressure of the contact and the D. C. characteristics. An upper limit of approximately 2 THz is established for electromagnetic field detection, with thermoelectric effects appearing as the frequency is lessened. Typical responsivity values of 100v/w at 90 GHz, 2v/w at 890 GHz, 10⁻²v/w at 28.3 THz, and 0.16v/w at 474 THz are presented with the latter two values being thermal in origin. A technique concomitantly presenting the T-V characteristic curve and the applied R. F. signal is shown to be extremely useful in maximization of the video response. Hardness data coupled with electron microscopy proves for the first time that the tungsten whisker is able to penetrate the silicon. Observed penetration is of the order of 0.1 micron or less and is hemispherical with a radius of approximately the same as the depth. A general discussion of the findings is given with interpretation of the new results.