Check out the companies making headlines after the bell: 

Micron Technology — The semiconductor stock slumped about 2% in after-hours trading after earnings and revenue for its fiscal first quarter fell short of Wall Street's expectations. Micron Technology also said it expects a wider-than-expected adjusted loss of 62 cents a share for the current period.

Under Armour — Under Armour's stock seesawed in extended trading following news that Marriott International President Stephanie Linnartz will join the athletics apparel company as its next CEO. Shares last traded about 1% lower.

MillerKnoll — MillerKnoll's stock jumped 6% in extended trading after the office furniture maker beat top and bottom line estimates for its fiscal second quarter. Guidance for the current quarter fell roughly in line with expectations from analysts surveyed by StreetAccount.

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