The incident happened around 10 p.m. Sunday at the Foothill Liquor on 400 block of W. Foothill Boulevard.
Police said the suspect, armed with a semiautomatic handgun, demanded the two employees inside the store open the cash register. While the robber was grabbing the money out of the register, one of the clerks tried to fight the suspect for the gun, according Rialto Police Lt. Joe Cirilo.
Officials said one clerk tried to fight the suspect for the gun.
"Unfortunately, the suspect fought back and he shot the clerk and eventually left the store with the money," Cirilo said.
The victim was taken to a hospital in critical condition.
The suspect fled the liquor store on foot, leaving a trail of money as he ran away. He was described as a black man in his 20s, about 5 feet 7 inches tall and 165 pounds. He was wearing a grey sweatshirt and blue jeans.
Residents in the neighborhood say they are worried about the crime in the area and refer to the liquor store as a friendly, neighborhood store.
"It's devastating because we come here every day and we talk to the owner here and a lot of the employees that work here, and they're really nice people. Really good people," said Danielle Martinez.
Anyone with information was asked to call the Rialto Police Department at (909) 820-2550.