Low residual stress silicon oxynitride thin films are investigated for use as a replacement for silicon dioxide (SiO2) as sacrificial layer in surface micromachined microelectrical-mechanical systems (MEMS). It is observed that the level of residual stress in oxynitrides is a function of the nitrogen content in the film. MEMS film stacks are prepared using both SiO2 and oxynitride sacrificial layers. Wafer bow measurements indicate that wafers processed with oxynitride release layers are significantly flatter. Polycrystalline Si (poly-Si) cantilevers fabricated under the same conditions are observed to be flatter when processed with oxynitride rather than SiO2 sacrificial layers. These results are attributed to the lower post-processing residual stress of oxynitride compared to SiO2.