The average shear‐wave velocity within the top 30 m from the surface, VS30, represents site characteristics including the soil classification and site amplification that are essential information for building codes and seismic design. A novel method to determine a VS30 model based on a composite analysis of borehole standard penetration test numbers (SPT N) and horizontal‐to‐vertical (H/V) spectral ambient noise ratios is introduced. A national VS30 model for South Korea is determined using the method. The shear‐wave velocity structures beneath 20 nationwide broadband seismic stations are determined using the H/V analysis. The SPT N data are collected from 175,619 nationwide densely‐distributed boreholes. The shear‐wave velocity models from SPT N values are calibrated for the local reference velocity models from H/V analysis. A representative relationship between the SPT N values and shear‐wave velocities is introduced. A national VS30 model for South Korea is determined using the calibrated SPT N models at the nationwide boreholes. The VS30 model is verified by comparisons with local field measurements. The proposed model is consistent with the USGS model based on a surface slope analysis. The VS30 structure presents high correlation with geological and topographic features. The VS30 values are low in coastal (low topographic) areas, and high in mountain (high topographic) areas. Apparent linear relationship is observed between VS30 and topography. The western and southeastern coastal regions may be vulnerable to strong seismic shaking. Plain Language Summary Seismic ground motions are an important factor to control the seismic damages. The seismic amplification is highly dependent on the shear‐wave velocities at shallow depths  ≤30 m, VS30. We introduce a novel method to determine a VS30 model based on the standard penetration test numbers (SPT N) from nationwide 175,619 boreholes and horizontal‐to‐vertical spectral ambient noise ratios (H/V ratios) from 20 broadband seismic stations. We determine a VS30 model for South Korea. The shear‐wave velocity structures beneath broadband seismic stations are used for local reference velocity models. The shear‐wave velocity models from SPT N values are calibrated for the local reference velocity models from the seismic stations. We determine a representative relationship between the SPT N values and shear‐wave velocities. We determine a high‐resolution VS30 model using the calibrated SPT N models at boreholes. The proposed model is verified by comparisons with other results. The VS30 structure presents high correlation with geological and topographic characteristics. The VS30 values are low in coastal areas, and high in mountain areas. The western and southeastern coastal regions may be vulnerable to strong ground motions during earthquakes. Key Points A novel method based on SPT N values and H/Vratios is proposed for determination of national VS30 model for South Korea A high‐resolution national VS30 model can be calculated using the calibrated SPT N data at densely distributed boreholes The VS30 model presents high correlation with geological and topographic features