This manuscript describes two MEMS based optical sensors for wall shear stress and velocity measurements in flow fields. Experimental results obtained with the wall shear stress sensor, the MicroS³, are compared with boundary layer velocity measurements obtained with a traversing laser Dopplere anemometer. Preliminary velocity measurements conducted with the time-of-flight Micro Velocimter, the MicroV, in a microchannel indicate that these microsensors offer a wide range of opportunities for the implementation of chip function monitoring and feedback control loops on microfluidics chips. Future sensor designs are described.