An interposer, including a redistribution layer structure, first conductive terminals, and second conductive terminals, is provided. The first conductive terminals are disposed on a first surface and are electrically connected to the second conductive terminals. An orthographic projection area of the first conductive terminals on the redistribution layer structure is inside a circuit range outline. There is a first pitch between the adjacent first conductive terminals. The second conductive terminals are disposed on a second surface. An orthographic projection area of a first part of the second conductive terminals on the redistribution layer structure is inside the circuit range outline. An orthographic projection area of a second part of the second conductive terminals on the redistribution layer structure is outside the circuit range outline. There is a second pitch between the adjacent second conductive terminals. The second pitch is greater than the first pitch. A semiconductor package is also provided.