Smart devices (or things) in the realm of IoT (Internet of Things) talk to each other and transfer data over the Internet.IoT vendors provide APIs for their clients to send data to the gateways and application servers. However, there is a lack of guidelines on how a vendor would design its API and resource URIs (Uniform Resource Identifiers). A generic design solution –design patterns– would make the API design and development easier for the vendors. Design patterns are reusable solutions to recurring problems and provide improved reusability and understandability. Currently, there are no design patterns for URIs of IoT APIs that IoT vendors can use. In this paper, we analyzed more than 1,300 URIs from 13 IoT APIs including IBM Watson and Microsoft Azure, and proposed eight novel design patterns for URIs of IoT APIs. We analyzed one dataset divided into two subsets: (1) analysis set with 70% of all our URIs to define design patterns for URIs of IoT APIs and (2) validation set with the remaining 30% of the URIs to verify the prevalence of the defined design patterns. We could map 84% of our validation set to the defined design patterns, i.e., design patterns are prevalent in the IoT domain.