Methods of forming decoupling capacitors in interconnect structures formed on backsides of semiconductor devices and semiconductor devices including the same are disclosed. In an embodiment, a device includes a device layer including a first transistor; a first interconnect structure on a front-side of the device layer; a second interconnect structure on a backside of the device layer, the second interconnect structure including a first dielectric layer on the backside of the device layer; a contact extending through the first dielectric layer to a source/drain region of the first transistor; a first conductive layer including a first conductive line electrically connected to the source/drain region of the first transistor through the contact; and a second dielectric layer adjacent the first conductive line, the second dielectric layer including a material having a k-value greater than 7.0, a first decoupling capacitor including the first conductive line and the second dielectric layer.