To develop a convenient and simple low-level alpha contamination monitoring method for large quantities of radioactive wastes, a foil-type electret dosimeter was examined. For the electret material, fluoride polymer was used, and the polymer foils were charged and polarized by applying a high voltage in air while heating at ∼150°C. The surface charge density of the electret foil before and after irradiation was measured by converting to a piezoelectret signal through use of a polyvinylidene fluoride. In the experiments, using a 2.5 kV/mm electric field in electret foils, an electron avalanche effect was produced, and surface charge decay was multiplied. The maximum multiplication factor obtained was ∼200. The detection limit of alpha surface contamination was confirmed as 10−6 μCi/cm2 (3.7 × 102 Bq/m2) for a 5-h irradiation time.