The nucleation efficiency of a thermal ink jet printhead is improved by forming a heater element with a planar surface. A heater resistor, polysilicon in a preferred embodiment, has an irregular surface which can trap gas or vapors in the cracks or crevices. When the heater resistor is pulsed, the nucleation temperature is reduced by these trapped vapors requiring an increase in electrical input to the resistors, thereby reducing efficiency. The invention recognizes that a heater resistor with a planar surface in contact with an ink layer results in a higher nucleation temperature and increased efficiency. In one embodiment, a phosphosilicate glass (PSG) is flowed directly onto the resistor surface forming a planarization layer. Subsequent deposition of tantalum substantially replicates the underlying topography creating a heater resistor with a smooth surface adjacent the ink.In a second embodiment, a diffusion layer which is conformal is formed on the resistor surface with the PSG layer formed on the oxide layer. The diffusion layer can be a pyrolytic CVD deposited silicon nitride or a thermally grown oxide layer. The PSG layer has a planarized surface to which the tantalum conforms.