Nonvolatile flash memory technology is widely used in our daily life. Following the recent progress in silicon photonics, there is now an opportunity to embed flash memories also in photonic applications. As of today, chip scale photonic devices, e.g., micro‐resonators, are becoming essential building blocks in modern silicon photonics. However, their properties, such as their resonance frequencies, fluctuate due to fabrication tolerances, significantly limiting their applicability. Here, by integrating the well‐established non‐volatile flash memory technology into silicon photonic circuitry, this major obstacle is tackled and electrical post trimming of such resonators is demonstrated. Specifically, the Metal‐Oxide‐Nitride‐Oxide‐Silicon (MONOS) structure is used to trap charges in the thin silicon nitride layer, located in close proximity to the silicon device layer. This enables accumulating charges in the silicon, modifying the effective index of the optical mode and consequently the resonance frequency. By doing so, a robust and CMOS compatible nonvolatile memory solution is provided, which not only allows for precise trimming of the resonance frequency of the photonic device, but can also be easily manufactured and commercialized. This approach paves the way for efficient utilization of photonic structures such as resonators and interferometers in chip scale silicon photonics and electro optic systems, with a wide range of applications spanning from filters, switches and modulators, to sensors, and even lasers.