Goldman Sachs downgraded Micron to neutral from buy on Wednesday, sending the shares tumbling in premarket trading and further exasperating a violent sell-off in memory chip stocks this month.

The investment bank's analyst Mark Delaney cited "incremental weakness in both DRAM and NAND fundamentals per our discussions with industry contacts, and also based on our supply/demand analysis."

"Memory downturns usually last for several quarters and can see an acceleration in price declines, as customers delay procurement to wait for lower prices when possible, causing a snowballing effect that can lead downturns to be worse than initially anticipated by investors," Delaney said in a note to investors.

Micron shares tumbled 5 percent Wednesday and are now down 12 percent in one week through Tuesday.

Certain chip stocks have tumbled since last week when KLA-Tencor warned at a conference about weakness in the memory chip market. Along with Micron, KLA shares are off by 11 percent in one week through Tuesday.

— CNBC's Michael Bloom contributed to this story.