The robbery happened just after 1:00 p.m. Thursday at the Metro PCS store in the Newark Shopping Center at 230 East Main Street.
Police say the suspect entered the store and went to the rear of the business, where he confronted an employee with a gun.
Police say the suspect then forced the victim to hand over the money from the store register.
The suspect was last seen fleeing on foot south across East Main Street towards East Delaware Avenue.
The suspect is described as s black male, late teens to early 20's, goatee, thin build, wearing a royal blue hooded sweatshirt, jeans and sneakers.
Anyone with additional information about this incident should contact Detective Fred Nelson 302-366-7110 ext. 136.