B737-700
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Communication Breakdown
Conflict Ground Conflict; Less Severe; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Issued New Clearance
Environment - Non Weather Related; Human Factors
While #1 and holding short of MDW Rwy 22L; we heard a takeoff clearance what we thought was our call sign and flight number. We accepted the clearance and read it back. As I turned on lights and began rolling onto the runway; I saw another aircraft on the other side of the runway taking the runway as well. In the darkness of night and the many lights effectively camouflaged the other aircraft. Neither my First Officer or I had seen the other airplane and were not even aware of its presence until that moment. I immediately stopped the aircraft and asked tower who the take off clearance was for. Tower advised that it was for the Lear Jet which had similar sounding call sign and number and instructed us to hold short. We advised tower that we had crossed the Hold Short line. Tower instructed us to cross the runway; do a 180 turn and again hold short. We departed normally after the next arrival.
[Report narrative contained no additional information.]
B737 flight crew reported a runway incursion when they misunderstood an ATC clearance for an aircraft with a similar call sign.