It could be that your data values are not much different, so semilogx or semilogy may not seem different.
To test that hypothesis, try this and see if there is a difference between the figures:
x = linspace( 1, 10,10);
y = logspace(-2, 2, 10);
figure
plot(x, y)
grid
figure
semilogy(x, y)
grid
Experiment to get the result you want.
