The station signed on the air on June 1, 1961 as KOA-FM; the station first broadcast middle of the road (MOR) and later a beautiful music format. The radio station was co-owned with KOA-TV (Channel 4). Studios were located at 1044 Lincoln Street. In 1968 KOA Radio and TV were purchased by General Electric Broadcasting. By 1974 KOA-FM would flip to Top 40 as KOAQ "Q103," where it would enjoy a successful run and become one of Denver's top-rated stations during the early 1980s. Jack Regan was the station's long-time program director and morning DJ. Alan Sledge was music director, and held down the mid-day shift. He later added assistant PD duties. In late 1983 General Electric sold KOA and KOAQ to Belo Corporation of Dallas for $22 million. Lee Larson was selected as the new General Manager. He came to Denver from KLOS in Los Angeles. In 1987 Jacor Communications purchased KOA/KOAQ for $24 million. After nearly 14 years playing Top 40 or Contemporary hit radio, on January 18, 1989 they would flip formats to classic rock and adopt the KRFX call letters, becoming "103.5 The Fox", one of several stations in the U.S. using the brand "The Fox".
In late 1995 when KBPI began playing mostly new rock, Jacor sister FM KRFX added more newer hard rock as Steve Cooper of KBPI replaced Tom Little at night.
KRFX personalities include: Rick Lewis mornings; Colfax middays; and Roger King evenings. On Sunday evenings, the station carries the regionally syndicated Strictly Blues with host Kai Turner. The station also holds the local FM rights for the play-by-play for the Denver Broncos, sharing the games with sister station KOA (850).