Observation of the spin signals in devices with low interface resistance of ferromagnetic/semiconductor junctions is one of the most important issues from the application view point. We demonstrate spin transport and accumulation signals in highly doped ∼1×1020 cm-3 n+-Si by using CoFe/MgO/n+-Si (10 nm, 20 nm)/n-Si devices. The highly doped n+-Si was confined within a thin n+-Si layer (10 nm and 20 nm in thickness). In this confined structure, we observed the spin accumulation signals for the devices with impurity concentration of ∼1×1020 cm-3 and the spin transport signals for the devices with ∼1 kΩμm2 interface resistance. This indicates that the n+ confined structure is important for observing and increasing spin signals in the low-interface-resistance region.