Microcantilever arrays have been shown to be promising label-free nanomechanical sensing devices with high sensitivity. Two factors that affect the usefulness of microcantilevers in sensing scenarios are the sensitivity of the transduction method for measuring changes in microcantilever properties and the ability to create large compact arrays of microcantilevers. In this dissertation, we demonstrate that microcantilevers with an in-plane photonic transduction method are attractive because they maintain the sensitivity of the traditional laser beam reflection method while being scalable to simultaneous readout of large microcantilever arrays. First I demonstrate the integration of a compact waveguide splitter network with in-plane photonic microcantilevers which have amorphous silicon strip loading differential splitter and simultaneous microcantilever readout with an InGaAs line scan camera. A 16-microcantilever array is fabricated and measured. Use of a scaled differential signal yields reasonable correspondence of the signals from 7 surviving released microcantilevers in the array. The average sensitivity is 0.23 µm-1. To improve the sensitivity and consistency, and reduce fabrication difficulties, a new differential splitter design with 4 µm long double-step multimode rib waveguide is introduced. Furthermore, a modified fabrication process is employed to enhance the performance of the device. A new 16-microcanitiler array is designed and fabricated. The sensitivity of a measured 16-microcantilever array is improved to approximately 1 µm-1, which is comparable to the best reported for the laser reflection read out method. Moreover, most of the microcantilevers show excellent uniformity. To demonstrate large scale microcantilever arrays with simultaneous readout using the in-plane photonic transduction method, a 64-microcantilver array is designed, fabricated and measured. Measurement results show that excellent signal uniformiy is obtained for the scaled differential signal of 56 measured microcantilevers in a 64-array. The average sensitivity of the microcantilevers is 0.7 µm-1, and matches simulation results very well.