In a method for manufacturing ceramic substrates and module components, an unfired mother ceramic substrate is cut at predetermined positions for division into separate unfired ceramic substrates. The cut unfired mother ceramic substrate is pressed such that pressure is applied parallel or substantially parallel to its main surfaces so that the cross-sectional end surfaces created in the cutting step are joined. The unfired mother ceramic substrate including end surface junctions, resulting from joining of the cross-sectional end surfaces, is fired. The fired mother ceramic substrate is broken along the end surface junctions to divide it into separate ceramic substrates.