How to increase PR for inner pages?

Hi.

I have website that is ranked high in all Search engines and is doing quite well for all relevant keywords. The PR of homepage is also quite acceptable i.e. PR4. My only concern is that PR of none of the inner page is higher than one. There are 4 inner pages and only one has PR 1 rest all are PR 0. I don’t know what’s wrong with the Google and why my inner pages do not have any PR. Can anyone suggest any techniques to increase PR of inner pages? Cheers!!

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