A parent or master substrate for a semiconductor package is provided, which can provide a plurality of unit substrates by cutting into pieces for producing a semiconductor device. The parent substrate includes an insulation layer, conductor patterns formed on first and second surfaces of the insulation layer, and PSR (photo solder resist) layers respectively formed on the first and second surfaces of the insulation layers and covering the conductor patterns. The parent substrate includes an upper part and a lower part divided by a reference surface which passes through the center of the insulation layer. When an equivalent thermal expansion coefficient αupper of the upper part is defined by the Equation of α upper = ∑ i = 1 n ⁢ α i × E i × v i ∑ i = 1 n ⁢ E i × v i , where αi is respective thermal expansion coefficients of, Ei is respective elastic moduli of, and vi is respective volume ratios of first through nth components constituting the upper part (e.g., insulation layer, conductor patterns, and PSR layers of the upper part), and an equivalent thermal expansion coefficient αlower of the lower part is defined by the Equation of α lower = ∑ j = 1 m ⁢ α j × E j × v j ∑ j = 1 m ⁢ E j × v j , where αj is respective thermal expansion coefficients of, Ej is respective elastic moduli of, and vj is respective volume ratios of first through mth components constituting the lower part (e.g., insulation layer, conductor patterns, and PSR layers of the lower part), a equivalent thermal expansion ratio (αupper/αlower) of αupper to αlower is selected to be within a range of 0.975 through 1.165.