The heat treatment of metallised compound semiconductors results material diffusion and evaporation, called volatile component loss. In situ SEM and mass spectrometric study showed, that surface pattern has fractal character at heat treatment temperatures, where the volatile component loss has maximum value. The so-called fractal dimension or scaling factor of self-similarity (D) was evaluated for Au/lnP (D = 1.57 +/- 0.01), Pd/InP (D = 1.75 +/- 0.01) and Au/Pd/InP contacts. The comparison of SEI and BEI images suggested that the geometrical surface patterns, resulted by the balling-up phenomenon, and the pattern, which possible describes the phase inhomogeneity on the same contact, can be characterised by different values of the fractal dimension. In the case of the studied Au/Pd/InP contact, D was 1.56 +/- 0.02 for balling up and D was 1.84 +/- 0.01 for phase distribution.