The electrical properties of p-type layers of InP, formed by the diffusion of zinc into n-type material, are studied. A wide range of diffusion conditions are used and both homogeneously doped specimens and those containing a zinc atom concentration gradient are produced. The impurity atom distribution of the diffused crystals is characterised by radiotracer analysis. p− n junction measurements on non-homogeneously doped specimens indicate that the number of zinc atoms in a diffused layer is much greater than the number of shallow acceptors. This non-correspondence of atom and carrier concentrations is confirmed by four point resistivity, Hall effect and capacitance-voltage measurements. The first two of these techniques are used to produce carrier concentration profiles which are compared with corresponding radio-tracer profiles. The carrier profiles are achieved by both serial sectioning and multiple specimen techniques. A gold probe point contacting procedure is developed for the Hall Effect measurements from which a plot of carrier mobility versus carrier concentration, in the range 5 × 10 18 – 5 × 10 19 cm −3, is produced for p-type InP.