We experimentally demonstrated slow-wave-enhanced phase and spectral sensitivity in asymmetric Michelson interferometer (MI) sensors. Compared to Mach-Zehnder interferometers (MZI) that experimentally demonstrated a phase sensitivity of 84,000 rad/RIU-cm, the reflected path enhancement of the optical path length coupled with slow light enhancement with photonic crystal waveguides in on-chip slow light Michelson interferometer sensors resulted in experimentally demonstrated phase sensitivity of 277,750 rad/RIU-cm with theoretical phase sensitivity as high as 461,810 rad/RIU-cm, at the same form factor as the MZI of identical interferometer arm lengths.