The composition parameter x dependences of electrolyte electro-reflectance (EER) spectra were observed on a series of Ⅲ-Ⅴ group compound semiconductor alloy samples of GaAs

1-

x

p

x

and Al

x

Ca

1-

x

As."Three-point adjusting method"was adopted in the estimation-of critical point energies and its allied spin-orbit splittings E

g

o

△

o

E

g

1

△

1

. From the values of E

g

o

compositions of all GaAs

1-

x

p

x

samples were obtained according to a formula given in Ref [9]. Then

empirical formula of parabolic type for all of the energies [E

g

o

+△

o

](x)

E

g

1

(x)

[E

g

1

+△

1

](x) were achieved by a best fit procedure

In the circumstances of GaP(x=1)

a value of △

1

about 0.16eV was definitely measured. deviating appreciably from"2/3 rule" for the ratio of △

1

:△

0

.The necessity of applying a quabra-tic term correction to the linear type assumption of E

g

o

(x)

conventionally used in photovoltaic determination of the semiconductor alloy compositions

has been demonstrated.