A POSSIBLE RWY INCURSION DURING A NIGHT OP AS RPTED BY A S80 PIC AFTER LNDG RWY 19L AT SFO; CA.

Narrative

I WAS CAPT; PNF. FO LANDED ILS VISUAL RWY 19L AT SFO. I TOOK CTL OF ACFT; EXITED RWY AT TXWY G AND STOPPED. AFTER WAITING SEVERAL SECONDS WITH NO INSTRUCTIONS FROM TWR; I DIRECTED FO TO CONTACT GND ON 121.8 I HAD PRESELECTED. WE TOLD GND WE HAD JUST CLRED THE RWY; AND CTLR ANSWERED QUOTE; 'TAXI TO THE RAMP.' I TAXIED STRAIGHT AHEAD AND TURNED R ONTO TXWY A; PROCEEDING TO THE RAMP. AS I TAXIED ONTO TXWY A; IT OCCURRED TO ME THAT I HAD LANDED ON RWY 19L; AND WOULD HAVE CROSSED RWY 19R TO REACH THE INNER. WE HAD JUST CROSSED THE RWY WITHOUT A SPECIFIC CLRNC TO CROSS FROM EITHER TWR OR GND CTLR. I NOTED THAT NO AMBER HOLD LIGHTS OR WHITE RWY LIGHTS APPEARED TO BE ILLUMINATED ON RWY 19R. ATIS THAT HR DID NOT LIST RWY 19R AS AN ACTIVE RWY. I DID NOT SEE ANY ACFT IN POS ON TKOF ROLL OR SHORT FINAL FOR EITHER RWY 19L OR RWY 19R. I DO NOT BELIEVE ANY LOSS OF SEPARATION OCCURRED; HOWEVER; HOW EASILY THIS INCURSION COULD OCCUR HAS MY ATTN. SOME CONTRIBUTING FACTORS INCLUDE NARROW SPACING OF THE 2 RWYS; NEARBY RAMP LIGHTS MUCH BRIGHTER THAN TAXI AND RWY LIGHTS; CLEANUP CHKLIST ITEMS AS WE EXIT RWYS; AND INADEQUATE ARPT DIAGRAM REVIEW AT FAMILIAR ARPTS.