B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 36; Flight Crew Total 5953; Flight Crew Type 2935
Other / Unknown; Situational Awareness
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter CFTT / CFIT
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented
Human Factors
I was flying the ZZZZZ 2 XXR transition arrival into ZZZ with autopilot on and LNAV/VNAV PATH active. All altitudes and speeds were cross checked with the approach plate. ATC vectored us off the arrival and descended us from 9;000 to 8;000. ATC asked and we reported field in sight. We were then cleared direct to ZZZZZ (final approach fix for ILS) and the visual to XXR. I then had FO (First Officer) select 7;000 for final approach fix crossing per the approach plate. Just about the time I leveled at 7;000; and approximately 10 miles south of ZZZZZ; ATC issued a low altitude alert. We were still visual conditions and had not received an aircraft EGPWS terrain alert. At no time did I feel we were in an unsafe aircraft state. I then realized my error that I had departed 8;000 too soon. By descending to 7;000 when I did; I departed the lower limit of the Class B airspace for my location. We continued the approach and landed uneventfully.
Air Carrier Captain reported 'cleared for visual approach' then descending too low and receiving a low altitude alert from ATC.