A slice of silicon with specially patterned electrodes on each side was fabricated in an effort to make a particle radiation detector with a small active area. The active area was mapped out with the aid of a narrow collimated beam of van de Graaff generated protons and the area thus found is compared with the shapes of the electrodes on the faces of the slice. An attempt was made, by altering the bias condition on the electrodes, to improve the coincidence between the active area and the electrodes.