Ion implantation forn‐type doping of high‐density (CH)xfilms was studied experimentally. Apparent doping effects were observed in those films implanted with relatively low‐energy (12 keV) sodium ions. Current‐voltage characteristics of ap‐njunction produced between the implanted and original (p‐type) regions in a film exhibited a rectifying behavior for over 37 days. The improved stability in air was also observed. Doping by ion implantation is potentially useful to increase the life span of (CH)xdevices up to the point of practical use.