A very compact direct sunlight sensor is presented which uses 3 component solar cells in a fully molded package. The 3 Channel Isotype Sensor (3CS) is less than 10 cm long and less than 2 cm thick. A fused silica light guide is used for the optical path such that air filled cavities can be avoided completely. The sensor features an exchangeable front aperture which allows the adaptation of the opening angle of one or more channels to the acceptance angle of a CPV System. The sensor is described in detail and outdoor results are presented.