Ultra micro- or nano-indentation is now widely used to determine the hardness and modulus of thin films on various substrates. In this paper, spherical tipped diamond indenters of small radii are used to investigate the fracture behaviour and delamination of thin TiN films on silicon. The observations clearly establish that the initial behaviour is elastic but at a critical load a sharp discontinuity occurs in the force-displacement curves at the onset of film fracture. Associated with this deformation, the underlying silicon material experiences a pressure-induced phase transformation and film delamination occurs about the contact site. A simple fracture mechanics analysis is presented to estimate the interfacial fracture toughness of the TiN film on the silicon.