The effect of hexamethyldisilazane (HMDS) on adhesion between Parylene-C (Px) and silicon is investigated through the use of peel tests and contact angle tests. These tests allow measurement of the adhesive forces and investigation of the possible mechanisms for variations in adhesion that can be exploited in processes that require devices to be peeled from their substrate to release them after they are fabricated. An analytical framework is used to quantify the upper limit of adhesion on the basis of the geometric and material properties of a device. It was found that the modulation of adhesion between Px and Si by treatment with HMDS is largely due to the increase in dispersive surface energy of treated Si over the range 5.3-18.1 mJ/m2 based on measured contact angles of 46.3°-74.9° with DI water and 36.2°-55.7° with ethylene glycol. Varying the duration of HMDS vapor prime from 0 min to 2 min modulates the average adhesion between Px and Si from 5 mN/cm to 16 mN/cm.