Ultra-micro indentation using both pointed and spherical tipped indenters has been used to characterize mechanical properties of silicon nitride densified by glass encapsulated hot isostatic pressing (HIP). Young's modulus and hardness have been studied as a function of distance to the interface between silicon nitride and the encapsulation glass. The Young's modulus values are 10 to 20% lower in the close vicinity of the silicon nitride surface compared to bulk values. At distances of 75 to 150 microns from the glass-silicon nitride interface, bulk values are measured. The differences in hardness values between the region close to the surface and the bulk is less pronounced. A possible explanation for these gradients is formation of new phases at the surface of the silicon nitride. Routines for the calibration of both the pointed and spherical tipped indenters are presented