The track formation in semiconductors has been studied for over last ten years. The threshold electronic energy loss required to create tracks in semiconductors is relatively larger than in insulators. Among semiconductors, track formation in InP by monoatomic ion irradiation has been studied extensively. This work presents new results concerning the creation of tracks in a semiconductor, InP, irradiated at room temperature with energetic heavy cluster ions. Samples prepared for transmission electron microscopy (TEM) observations were irradiated with 23–40 MeV C60 ions at fluences of the order of 1010 ions cm−2. During the slowing-down of such projectiles in the targets, energy is mainly lost in electronic excitation and ionisation. It should be noted that the corresponding energy densities are one order of magnitude higher than those obtained using GeV monoatomic ions as projectiles, which leads to very strong structural modifications. Track diameters have been measured for three different ion energies and compared to previous results obtained with monoatomic ions. We also analyse our results using thermal spike model (TSM) proposed by Szenes for track formation and address its validity for such studies. The analysis highlights the doubt on the basic assumptions of the model and its applicability particularly for the case of cluster irradiations.