Both incidents occurred at 7-Eleven convenience stores in Wilmington an hour apart on April 22.
In the first incident, police say the suspect demanded money from the cash register. The victim complied and turned over an undisclosed amount of cash.
In the second incident, police say the suspect vaulted the sales counter and attempted to assault the clerk, then took cash from the register.
No one was injured in either incident. Police say the suspect covered his face with a T-shirt to conceal his identity.