Interfacial charge transfer from silicon to metal contact plays a key role in silicon-based electronics and optoelectronics. Surprisingly, a direct probe of this interfacial charge transfer process has not been investigated. Here we exploit the transient reflection spectroscopy to interrogate the charge transfer from silicon to platinum. We find that the charge transfer from silicon to Pt is extremely fast, which can also be drastically reduced and eventually shut by inserting silica spacing layers with increasing thickness between silicon and Pt. Our result suggests the possibility to extract carriers from silicon without losing their kinetic energy.