The present disclosure relates to a solid-state imaging element, a sensor apparatus, and an electronic device capable of achieving better characteristics. A transistor constituting a pixel includes: a gate electrode having at least two fin portions formed so as to be buried from a planar portion planarly formed on a surface of a semiconductor substrate toward an inside of the semiconductor substrate; and a channel portion provided across a source and a drain so as to be in contact with side surfaces of the fin portions via an insulating film. In addition, a width of the channel portion is formed to be narrower than a depth of the fin portion. The present technology is applicable to a CMOS image sensor, for example.