The pilot reported that during the landing rollout on a 3,001-ft-long, asphalt runway, he intended to retract the flaps, but instead he retracted the landing gear. The result was that all three of the landing gear assemblies retracted into their respective wheel wells during the landing roll. The lower fuselage stringers were substantially damaged. The pilot added that there were no preimpact mechanical malfunctions with the airplane. The airplane was equipped with a squat switch on the left main landing gear that was designed to prevent the landing gear from inadvertently retracting; however, the switch required that sufficient weight be on the landing gear in order to work effectively. The pilot stated, and a video of the landing confirmed, that the airplane was still moving at relatively high speed when he selected the landing gear handle to the retracted position. The pilot reported that the squat switch was tested at the last annual inspection and that it operated normally during the inspection. Based on this information, it is likely that the airplane’s wings were still generating lift when the landing gear handle was selected to the retracted position and the gear struts was not compressed enough to activate the squat switch.