Semipalmated plovers have plumage that alternates between the breeding and non-breeding season.

Between March and August, the breeding season (or alternate plumage) is displayed. The upper part of their body is brown and the underparts are white. Near the breast is a black band that circles around the neck, above which is a white collar that extends to the bill. A white spot is located between the black eyes, which are lined with a yellow-orange ring. The bill is short, with a yellow-orange base and a black tip. The legs are a dull yellow or orange. Females can be distinguished by the brown feathers on their faces and breast-bands, while males have more orange on their bills.

During the non-breeding season, from September until February, their basic plumage is displayed. Here, the black banded plumage on the head and breast is replaced by gray and brown and a white stripe that goes past their eyes, sometimes combining with the forehead. The bill also changes colors; the yellow-orange becomes duller, and the blackness spreads from the tip to the base. It is harder to differentiate between males and females in winter, but males have blacker heads.

Semipalmated plovers reach lengths of 6.7 to 7.5 inches (17 to 19 centimeters) and weigh about 1.7 ounces (50 grams, or about the weight of two AA batteries). Their wing length averages 4.7 to 5.1 inches (12 to 13 centimeters).

They nest in sand or gravel ridges, beaches, or dry vegetated ground. While migrating, they inhabit sandy beaches, mudflats, flooded fields, salt marsh pools and shorelines.

Semipalmated plovers live up to nine years in the wild.

Semipalmated plovers use a variety of vocalizations to communicate. They have a standard call note that sounds like a whistled chu-wheet.  They also have different calls to attract a mate or to sound an alarm about a threat nearby.

Additionally, they use movements to communicate. For example, they may fake an injury by fanning their tail, tilting their body, and partially opening their wings to distract humans or other predators and lure them away from their nest. Some will defend nesting or feeding territories by running, chasing, or pushing other birds aside.

During the breeding season and while migrating, they mostly eat invertebrates like shore flies, polychaete worms, amphipods, beetles, spiders and solider fly larvae. They tend to forage in wet or damp areas, like shorelines, flooded fields, or tiny pools of water from melted snow.  They primarily hunt using their vision, and if they see prey they will quickly peck or snatch it. They will otherwise stick their bill into the ground to probe for food. Semipalmated plovers will also stir their feet in muddy water to locate prey. They use the wintertime to gain extra body weight, which provides them with enough energy to make their spring migration.

Semipalmated plovers are active during the daytime. Not all semipalmated plovers will sleep at night; some will forage after dark.

Semipalmated sandpipers are generally not social during the breeding season. While migrating and roosting, they can form small flocks of a few individuals to larger flocks of 200 to 600 birds. Some unusually large flocks have been reported in coastal South America, with up to 4,000 birds.

Males are the first to arrive at the breeding locations in the sub-Arctic and southern Arctic regions. The males establish territories along rivers, beaches, ponds, lakes and peaty areas by digging out a shallow nest, or a scrape, in well-drained bare sand or gravel. Occasionally, they will nest on moss carpets or lichen. The females arrive shortly after and sit in the scrape of the male she chooses to mate with, forming a pair. They line the nest with whatever material is nearby: rocks, shells, leaves, charcoal, seaweed, grass, sand, glass and woody debris. Females will lay four eggs that are light brown or pale olive and covered in black or brown blotches.

The pair takes turns incubating the eggs, rotating every two to four hours until the eggs hatch after 23 to 25 days. The chicks are brooded for five days after hatching. The female abandons her offspring after 15 to 25 days, and the male becomes the sole protector of the chicks. The chicks may be led by their parents to a lake for feeding, but they find food by themselves. The chicks can walk within hours of hatching and fly within 23 to 31 days.

Juveniles display plumage like adults in the non-breeding season. Their bills are entirely black, and the white is more widespread. The breast band is narrower than in adults. Feathers on their upper wings may have pale brownish-yellow or gray margins.

Many shorebird populations are declining. Some threats to semipalmated plovers include habitat loss especially along coastlines during migration and wintering, collisions with structures, and subsistence hunting.