Typical frequency drift rates of type III solar radio bursts over a wide range of frequencies have a power law dependence with frequency (Alverez and Haddock, 1973). Typical excitation times and decay times also show a power law dependence on frequency (Fainberg and Stone, 1974). We derive these fundamental characteristics of satellite-observed type III bursts by assuming that time and frequency form a single self-similar parameter, which we use to express time variation of the radiation intensity from an individual source. Comparisons of our theoretical profiles with observed intensity profiles are presented.