It happened at 5th and Raymond streets around 12:30 a.m. Friday.
Police say at least seven shots were fired from two sides of the street.
Police arrested a 22-year-old man believed to be involved in the exchange of gunfire.
Investigators found the 20-year-old victim several blocks away on the 4500 block of Reese Street.
He was taken to Temple University Hospital in critical condition with a gunshot wound to the leg.
They do not know if he was the second gunman, or if there is another armed person on the run.