On March 21, 1994, at 0200 mountain standard time, a Beech 95- C55, N9415S, operated by Northern Colorado Air Charter, landed gear up at the Gillette Airport, Gillette, Wyoming. Visual meteorological conditions prevailed at the time and an instrument flight rules flight plan was filed. The airplane was substantially damaged and the certificated airline transport pilot and his two passengers were not injured. The flight was conducted under 14 CFR 135 that departed from Denver, Colorado, at 0005 on March 21, 1994. The pilot reported that a straight in approach for runway 34 was planned. The pilot reduced power and selected gear down. The pilot stated that he felt the landing gear coming down and called gear down. The approach was continued and just before touchdown, the pilot noted that the gear selector was down, however, the green gear light for the down and locked position was not illuminated. The pilot added power, however, the left side propeller contacted the runway and the pilot reduced power and landed the airplane with the landing gear retracted. During the post crash inspection, the airplane was jacked up and a gear cycle test was performed. It was found that the gear selector switch worked intermittently. The landing gear was cycled six times and one out of the six cycles of operation, the landing gear failed to extend. Further inspection revealed that the gear warning horn was inoperative. The aircraft maintenance logs indicate that on December 3, 1993, the airplane was signed off for an annual inspection. The entry indicates that the gear warning horn was inoperative as connected to the throttles. An entry following the annual inspection, dated the same date, indicates that the throttle warning horn was connected and tested for proper operation.