<p>This paper derives the semi-analytical solutions for the direct current (DC) electric field, electric potential, and current excited by a point current source at an arbitrary depth in a horizontal layered geoelectric model. In existing DC electrical methods, the traditional apparent resistivity formula is only applicable to scenarios with a current source on the ground surface. Although grid-based numerical simulation methods can calculate the electric field excited by a current source at any depth, they suffer from large computational load and high cost. The method proposed in this paper enables more efficient calculation of the electric field excited by a current source at an arbitrary depth. In this study, the electric field is expanded using orthonormal and complete vector basis functions, and the electric potential is expanded using scalar basis functions. The field equations are transformed into a system of first-order ordinary differential equations in matrix form, and the semi-analytical solutions in integral form are obtained by solving these equations. The amplitude coefficients are determined using the generalized reflection and transmission method, and the integral values are numerically computed using the filter coefficient method.</p><p>The accuracy and reliability of the proposed method are verified by comparing with the closed-form analytical solutions of the electric potential and field in a homogeneous half-space, as well as with the results of traditional apparent resistivity calculations for horizontal layered media. Additionally, sensitivity analyses are conducted. The sensitivity analysis of the electric field to medium resistivity reveals that when the resistivity of a certain layer changes, the sensitivity increases as the current source is closer to that layer, reaching the maximum when the current source is located within the layer. The sensitivity analysis of the electric field to the water table shows that the sensitivity is significantly higher when the current source is above the aquifer and closer to it than when the current source is inside the aquifer. In addition, the traditional apparent resistivity formula is only applicable to surface sources. The method in this paper breaks through the limitation of source depth and fills the gap in the calculation of the electric field excited by underground sources.</p>