CHSU traces its origins to 1995 when the Canadian Radio-television and Telecommunications Commission (CRTC) granted Four Seasons Radio Ltd. a new FM licence for the Kelowna market offering country music. Its initial call letters were CKBL and its branding was 99.9 The Bullet. "The Bullet" signed on in October, 1995, and was the sister station of CKIQ, a news/talk radio station on the AM band that was owned by Four Seasons Radio Ltd. as well. In 1996, Okanagan Skeena Radio Group Ltd. acquired a number of radio stations in the Okanagan market when it bought out Four Seasons' parent company.
One year later, in 1997, "99.9 Sun FM" replaced "The Bullet" by offering a hot adult contemporary music format. Its call letters were changed to CHSU as well. Simultaneously, CKIQ changed its call letters to CKBL, which meant the Kelowna market lost a news/talk radio station leaving cross-town competitor CKOV as the sole station offering that format. CKBL continued to offer country music on the rebranded 1150 AM The Bullet.
In 1999, Telemedia acquired Okanagan Skeena Radio Group Ltd. along with other radio assets across the country. In 2002, Standard Broadcasting acquired Telemedia's radio assets. Standard later sold some stations in other provinces to various companies but it has retained its British Columbia stations and 99.9 Sun FM continues to operate with the same format and branding.