RWY INCURSION.

Narrative

AFTER CLRING RWY 17L ON H1; WE WERE ASSIGNED TO HOLD SHORT OF RWY 17R ON TXWY 27 ON TWR FREQ 126.55. THE CAPT CALLED FOR THE AFTER LNDG CHKLIST AFTER I CORRECTLY READ BACK OUR HOLD SHORT CLRNC. BEING NEW ON THE ACFT (40 HRS) MY EYES WERE FOCUSING IN THE COCKPIT FOR THE MOST PART. I LOOKED UP DURING THE CHK AND SAW THAT WE WERE AT TAXI SPD ABOUT 5 FT FROM THE HOLD LINE. IN THE TIME IT TOOK ME TO SAY 'HOLD SHORT' AND WE BOTH MADE SURE THERE WAS NO TFC ON THE RWY; WE WERE ABOUT 30 FT ONTO THE RWY. AT FIRST; THE CAPT DOUBTED MY INTERP OF OUR CLRNC. WE CONTINUED TO CROSS THE RWY WHEN TWR TOLD US TO THEN CROSS. THEY WERE AWARE WE HAD NOT HELD SHORT. IN ORDER TO STOP THIS FROM HAPPENING IN THE FUTURE; I WILL DELAY PERFORMING ANY CHKLISTS UNTIL WE ARE CLR OF RWYS OR AT A STOP. CONTRIBUTING FACTORS INCLUDED: LACK OF SLEEP -- IT WAS THE LAST LEG FOLLOWING APPROX 5 HRS OF SLEEP. LOW TIME IN ACFT -- I HAD MY HEAD IN THE COCKPIT MORE THAN DESIRED DUE TO UNFAMILIARITY. NO TFC ON RWY/FINAL -- THE CAPT CLRED OUTSIDE; BUT FAILED TO HOLD CORRECTLY. OVERCONFIDENCE -- CAPT DOUBTED MY INTERP OF OUR CLRNC. NEVERTHELESS; WE SHOULD HAVE STOPPED ABRUPTLY AND THEN QUESTIONED TWR.