The intensive and improper use of antibiotics has dramatically increased the frequency of resistance among human pathogens and led to a global crisis of antimicrobial resistance. Thus, there is an urgent need to develop rapid diagnostic methods. In this work, we present a prototype device for rapid antimicrobial susceptibility testing (AST) using photonic silicon chips which provide both a preferable solid-liquid interface for bacteria networking and a simultaneous optical transducing element for monitoring bacteria upon exposure to antibiotics in real-time. The latter is achieved via intensity-based reflectometric interference spectroscopic measurements, referred to as iPRISM. First, we determine the iPRISM breakpoint concentration for American Type Culture Collection strains using known standard breakpoints produced by the Clinical & Laboratory Standards Institute to differentiate between resistant and susceptible bacteria. Next, we demonstrate that iPRISM can robustly differentiate between resistant and susceptible clinical isolates of Escherichia coli and Staphylococcus aureus within <90 min, as opposed to next day results of current clinical techniques.