The present technique relates to: a solid-state imaging element which is capable of preventing decrease in the light reception sensitivity of an avalanche photodiode; an electronic device; and a method for manufacturing a solid-state imaging element. This solid-state imaging element is provided with: an avalanche photodiode that comprises a first region of a first conductivity type and a second region of a second conductivity type, which is different from the first conductivity type, respectively extending in the thickness direction of a semiconductor substrate and an avalanche region that issandwiched between the first region and the second region; and a film that is formed on at least one surface of the semiconductor substrate, and is formed of a metal oxide film, a metal nitride film or a mixed crystal film of a metal oxide film and a metal nitride film. The present technique is applicable, for example, to a CMOS image sensor.