This contribution deals with surface micromachined BAW resonators based on AlN thin films. Process, design issues and first results are presented and discussed. Devices with two resonators in series having a resonance frequency between 7 and 8 GHz show promising results. Coupling coefficients of k/sub t//sup 2/ =3.8% and quality factors of 100 to 150 have been obtained with resonators having a approximate size of 30/spl times/30/spl mu/m adapted for a 50/spl Omega/ system. These results are clearly inferior to earlier results obtained with SMR designs (k/sub t//sup 2/=5.5% and Q=580). Reasons are too high serial resistances caused by bad step coverage of the top electrode, possibly also incomplete etching of the sacrificial layer, and warping by too large film stresses.