Asian Pear mummies
There are a few different diseases or insects that could cause this problem. Below I have posted some links to help you determine which yours might be.
More information would help to diagnose the problem. How healthy are the tree leaves? When you cut open the fruit, what do you see? Flesh discolored, insect larvae, etc. Damage visible on other fruit trees? Hopefully these links will help you and if it is still not clear, you can drop off a fruit and branch with leaves at the Linn Co. Extension office in Tangent and the volunteers at the Plant Desk will be able to assist you.
This is frustrating, but hopefully you will be able to use the pears anyway, unless the flaw is too deep in the fruit.
"Adults puncture fruit with their beaks and feed in the fruit flesh. The puncture may not be visible, but the surrounding area is sunken and often dark green. Beneath the skin is a group of loose spongy cells, often with brown discoloration. Damage looks similar to the disorder bitter pit, but bitter pit tends to be around the bottom of the fruit, while stink bug damage is typically around the top. Also, bitter pit produces a mass of corky brown cells beneath the skin, whereas the spongy cells caused by stink bug injury are only slightly discolored. Pome fruits tend to be damaged in late summer as they approach maturity."
PS, if you would like to bring us a sample, you can find us here: https://extension.oregonstate.edu/mg/linn-benton/have-gardening-question
Check out the tips in the signature tagline so you can bring us a sample that will help us to provide you with the best possible diagnosis of your issue!