Aluminum Nitride (AlN) based Surface Acoustic Wave (SAW) sensors have shown great application potentials on serving as biosensors. In this paper, we investigate the mass sensitivity of SAW sensors, which were fabricated based on Si/AlN structure by depositing aluminum oxide (AhO3) thin films on the active area between the input port and output port of the SAW devices. The material of the IDTs is aluminum. To validate the sample accommodation and protection function of the SiN thin film in bio-liquid detection processes, the contact angle of the SiN surface is also detected. We found that the mass sensitivity of the SAW devices is as high as 1958 MHz/g and the SiN surface is hydrophilic with contact angle of 45 degree. The research results indicate the AlN based SAW devices can be well employed in certain biosensing applications.@en